1. Field of Invention
This invention relates to savingS of 50% or more of shielding gas primarily in the MIG welding process while improving weld start quality.
2. Description of Prior Art
Gas metal arc welding (GMAW) is commonly referred to as metal inert gas welding (MIG). The term MIG welding is used for the purposes of this invention. In the MIG welding process molten metal is produced by an electric arc. This molten metal is derived from the materials to be welded and a filler wire. The filler wire is fed into the arc zone by a feeding mechanism. The molten weld metal is protected from the surrounding air by a shielding gas. A suitable power source is connected between the workpiece to be welded and to the filler wire passing though a welding torch. Welding power, welding filler wire and shielding gas are usually transported through the torch. The welding torch is usually attached to a flexible cable assembly and is manipulated by the welding operator.
The shielding gas employed to protect the molten metal formed by the electric arc can be a number of gases such as argon, carbon dioxide, and helium Mixtures of these and small amounts of other gases are employed to provide the desired welding performance. This shielding gas is often supplied in high-pressure cylinders, one associated with each weld station. Fabricating shops with a large number of MIG welders may have the shielding gas distributed to each welding machine through a delivery pipeline from a centrally located gas source. A pressure-controlling regulator is employed to reduce the shielding gas pressure contained in the high-pressure cylinder or in the delivery pipeline to a lower pressure level. When an inert type gas or gas mixture is used it is common for this pressure to be reduced to a preset level or 25 psig (pounds per square inch above atmospheric pressure), 30 psig, or in some common regulators designed for shielding gas delivery service, 50 psig. The exact fixed output pressure level of the regulator is dependent on the manufacturer and model. For installations using carbon dioxide as a shielding gas supplied in cylinders, it is common to employ a regulator with 80 psig fixed output. This higher outlet pressure reduces the possible formation of ice crystals in the regulator/flow control system as the carbon dioxide gas pressure is reduced. A variable flow control valve or suitable flow control device is incorporated immediately after the regulator or is built into the regulator mechanism. This flow control device allows regulation of the shielding gas flow to the appropriate rate needed for welding. The flow control device may incorporate a flow measurement gauge.
It is also common for a flexible hose to be used to deliver the shielding gas from the cylinder or gas pipeline regulator and flow control device to the welding machine or wire-feeding device. It is most common for this hose to be xc2xc inch in internal diameter. In some instances the hose may be {fraction (3/16)} inches in inside diameter. Some low current output welding machines, primarily designed for home use application, employ short lengths, usually less than 3 feet, of smaller diameter hose, small in internal and external diameter. To turn the flow of shielding gas on and off in commercial MIG welding systems, it is common to employ an electrically operated gas solenoid in the wire feeder or welding machine. A flexible hose connects the shielding gas supply to the solenoid at the welding machine. This hose is typically about 6 to 20 feet or longer in length to fit the needs of the welding installation. When welding is started, usually by means of an electrical switch on the welding torch, the gas solenoid is opened allowing shielding gas to flow through the welding torch to the weld zone. The electrical switch may simultaneously engage the wire feed mechanism and power source.
In most systems the flow of shielding gas is controlled by a flow control valve or other suitable flow control device at the regulator. The flow control device is adjusted to achieve the desired shielding gas flow. It is common for this flow to be set from 20 cubic feet per hour (CFH) to 40 CFH. Gas flows much in excess of this level can cause turbulence in the shielding gas stream as it exits the welding torch. This turbulence allows the surrounding air to be aspirated into the gas-shielding stream, degrading weld performance. In many systems, the pressure at the electrically operated gas solenoid needed to provide the proper flow of shielding gas is less than 5 to 10 psig. Therefore while welding is being performed, the pressure in the shielding gas delivery hose can be less than 5 to 10 psig.
While welding, the electric solenoid valve is open, and the gas pressure in the gas delivery hose is only that needed to establish the desired flow. The flow control device at the regulator is set for the desired shielding gas flow rate and indirectly establishes this pressure. This flow control device may incorporate a flow-measuring gauge to allow proper adjustment of shielding gas flow. Portable flow control gauges are also available. To use a portable gauge, it is put over the end of the torch, the wire feed mechanism is temporarily disengaged and the welding machine is activated with the torch held upward, away from the workpiece. The portable gauge is then used to set the proper shielding gas flow by adjusting the flow control device near the regulator. When the proper shielding gas flow is set and welding commences the pressure in the gas delivery hose near the solenoid is typically less than 5 to 10 psig depending on the torch type, length, and plumbing restrictions. When welding is stopped the solenoid closes and flow of shielding gas from the solenoid to the torch stops. However the gas flow continues to fill the gas delivery hose until the gas pressure in the hose reaches the pressure set by the regulator. The pressure in the gas delivery hose than rises from what was needed to establish the proper flow level to the outlet pressure of the regulator, typically 25 psig, 30 psig, 50 psig, or 80 psig as mentioned above. The excess pressure stores shielding gas in the gas delivery hose connecting the regulator/flow control device to the welding machine or wire feeder until the solenoid is opened again at the start of the next weld. Once the weld is restarted, this excess shielding gas is expelled very rapidly, usually within less than about xc2xd to 3 seconds. These shielding gas flow rates can momentarily reach in excess of 100 CFF, much higher than needed and also higher than desirable for good weld quality. Weld start quality can be impaired because of excess shielding gas flow creating air aspiration into the shielding gas stream. The wasted shielding gas, although small for each occurrence, can be very significant over time. Depending on the number of starts and stops versus the overall welding time, the wasted shielding gas can exceed 50% of the total gas usage. An article in the June 2000 Fabricator Magazine (referenced) sites the fact that most shops can reduce shielding gas consumption 50 to 80%. A significant waste is described as attributable to the excess storge of shielding gas in a commonly employed xc2xc inch inside diameter shielding gas delivery hose.
There have been devices sold which provide solutions to this problem:
(a) One device designed to reduce shielding gas loss is described in U.S. Pat. No. 4,341,237. This device is of complex construction involving several mechanical elements to store and control this excess shielding gas. When properly functioning, this device does accomplish the objective of reducing shielding gas waste. However, it has a number of interconnected parts and must be inspected periodically to assure gas does not leak from the numerous internal connections creating gas waste.
(b) Another method occasionally used to reduce gas surge upon the initiation of the welding arc is to incorporate a flow control orifice at the solenoid end of the shielding gas delivery hose. This device is sometimes sold with the intent to reduce gas waste. The device can give the perception that gas waste is eliminated since the momentary high gas flow surge at the start of welding is reduced, however the gas waste may still occur. Another possible way to incorporate such an orifice restriction is defined in U.S. Pat. No. 4,915,135. The orifice size is selected to restrict gas flow. Depending on the delivery pressure of the regulator these devices employ very small orifices, as small as about 0.030 inches. A filter is often employed to avoid these small orifices becoming clogged by metal flakes or dirt in the gas stream emanating from the cylinder or pipeline. However these devices are usually set to control the gas flow rate well above that desired. This is necessary since differing welding torches, torch lengths and internal plumbing restrictions require differing pressures at the solenoid to obtain the desired gas flow through the torch. The actual pressure needed at the solenoid is indirectly set at the flow control device usually located at the regulator as mentioned above.
Orifice restriction devices help reduce high flow gas surge at the weld start and the resulting degradation of the weld but often do not eliminate or significantly reduce shielding gas waste. The orifice size selected is usually significantly larger than needed to control the shielding gas flow at minimum needed levels. When welding has started, after a period of several seconds the flow-control device at the regulator determines the gas flow rate and indirectly the pressure at the solenoid valve. When welding, gas pressure in the shielding gas delivery hose at the solenoid valve end reduces to that needed to obtain the desired flow, for example for some torches and systems, 5 psig. This is usually significantly lower than the regulator fixed output pressure. At the end of welding, the gas solenoid closes and the pressure in the shielding gas delivery hose increases to the delivery pressure of the regulator, i.e. 25, 30, 50, or 80 psig. Once welding commences the restriction orifice in most instances is not reducing shielding gas flow to the level established by the orifice. After several seconds, the flow rate reduces to the lower level set at the flow control device near or built into the regulator. Therefore, the pressure in the welding gas delivery hose near the solenoid end reduces to the level needed to achieve the desired flow, perhaps 5 psig. Experiments show, once the solenoid valve is open at the start of welding, even when a typical flow restriction orifice is used in the system, a majority of the excess gas stored in the shielding gas delivery hose passes through the torch in about 3 seconds or less. Therefore, if the weld occurs for more than about 3 seconds in time, a similar amount of excess shielding gas is lost as if the restriction orifice was not present. The loss takes longer to occur, perhaps about 3 seconds, but it occurs. In addition, if the orifice were sized to restrict flow to exactly that needed by the system to achieve the desired flow, there is no excess shielding gas at the start. It is desirable to have some extra shielding gas at the weld start to purge the torch system of air. Air will diffuse into the torch system down stream of the solenoid from the open end of the torch when welding is stopped.
(c) Another method of reducing shielding gas waste is by reducing the volume of shielding gas stored in the delivery hose. Assuming a given length hose is needed to achieve the desired welding machine configuration, the other dimension controlling the volume in the shielding gas delivery hose is the internal cross sectional area. A system was introduced commercially which used a small inside diameter shielding gas delivery hose to reduce volume (see L-TEC publication referenced). However, this small inside diameter shielding gas delivery hose, 0.125 inch ID, was also small on the outside having an external diameter of 0.21-inches. This hose had only a 0.043-inch wall thickness. This system did not perform in the industrial environment to which it is subjected and was withdrawn from sale. This ratio of ID to OD hose size is typical of what is commercially available for small ID hoses designed for the pressure ranges involved. A typical xc2xc-inch inside diameter shielding gas delivery hose has an outside diameter of about 0.40 inches. This provides a hose with a wall thickness of about 0.075 inches. The larger outside diameter and thicker wall hose is much more durable in typical welding fabrication service than the smaller outside diameter hose. Standard commercially available small inside diameter hoses do not have the needed outside diameter and wall thickness to provide crush and abrasion resistance needed for a welding environment. The small outside diameter hose can also create more hose tangles in normal system use. Some small home use MIG welders do employ a small inside as well as outside diameter hose to deliver shielding gas very short distances from a small cylinder to the welder. This distance is usually less than 3 feet. These hoses are approximately 0.18 inch outside diameter and are unacceptable, in an industrial environment.
It is the principle object of the present invention to provide a means of delivering shielding gas to a MIG welding machine from a shielding gas source such as a high pressure cylinder or gas pipeline which minimizes the storage of shielding gas when the system is stopped and avoids wasted shielding gas each time the system is energized. This system can be used on most industrial MIG welders to obtain significant savings in shielding gas usage. It can be readily added to an existing installation as well as incorporated into new products. The system is designed to be simple, rugged, reliable and require little or no maintenance in an industrial environment. Since a significant amount of shielding gas is saved, fewer cylinders require changing in a given work period where high-pressure cylinders are employed. The wasted time required to change cylinders is reduced and productivity of the welder increased. In addition to the gas savings, the gas flow surge at the start of welding is significantly reduced. This reduces the possibility of air aspiration in the shielding gas stream and resulting poor weld starts. Some additional shielding gas is still provided at the weld start to purge any air that will have backed into the end of the gas hose in the welding torch.
The shielding gas delivery hose in this invention shall have a small inside diameter to reduce shielding gas waste but be of sufficient outside diameter and robustness to be usable in a welding environment and incorporate a surge flow-restriction orifice or small diameter hose connection device located at the end closest to the gas solenoid.